40 Fun Facts About Infrared

Which mammal uses infrared-sensitive receptors on its nose to home in on its prey's body heat?

The vampire bat has heat receptors on its nose-leaf that are thought to guide it to where blood flows closest to the skin. It is the only mammal known to feed entirely on blood.

The infrared flash from a TV remote, invisible to the naked eye, shows up on the screen of which gadget?

A smartphone shows the flash because its camera registers the coded flashes of light that human eyes cannot see. Each button press on the remote sends out a fresh stream of them.

Infrared scans found a hidden portrait of a bearded man beneath The Blue Room, painted by which artist?

Pablo Picasso painted The Blue Room in 1901 as a struggling 19-year-old in Paris who could not afford a new canvas for every idea, so he reused old ones.

Which Nintendo console's Sensor Bar is really a row of infrared LEDs that the handheld controller tracks?

The Wii puts five infrared LEDs at each end of its Sensor Bar, and an image sensor inside the remote watches those points of light to work out where it is aimed.

Infrared night-vision goggles show an image in which single colour, judged easiest to view for long periods?

Green was chosen because it was considered the easiest colour to look at for long spells in the dark. The goggles turn faint light into electrons, amplify them, then turn them back into a visible image.

The jewel beetle Melanophila acuminata uses infrared-sensing organs to find what, where it lays its eggs?

Forest fires draw the beetles in huge swarms to lay eggs in freshly burnt wood, and adults keep returning to the charred timber for up to a year.

Which NASA space telescope, launched on Christmas Day 2021, studies the early universe in infrared?

James Webb works in infrared because light from the earliest galaxies has been stretched out of the visible range on its long journey. A five-layer sunshield keeps the telescope cold.

Firefighters carry thermal imaging cameras because infrared lets them see people and hot spots through what?

Smoke hides flames and people from the eye, but a thermal camera turns their heat into a visible picture, letting crews find victims and the seat of a blaze quickly.

Which German-born British astronomer discovered infrared in 1800 by splitting sunlight with a prism?

William Herschel found that warmth kept increasing past the red end of the spectrum, where no light could be seen. He had first come to Britain from Hanover as a musician.

Which device, placed just past the red end of a prism's spectrum, revealed infrared with a rising reading?

A thermometer placed just outside the red light showed a rise in temperature, revealing rays nobody could see. The experiment had set out to measure the heat of each colour.

What does the Latin prefix infra mean in infrared, describing where the rays sit relative to red light?

Below is the meaning: the rays sit just under red light in frequency and energy. Infrasound, sound pitched too low to hear, borrows the same prefix.

Rattlesnakes strike warm prey in total darkness using infrared organs that give which snake group its name?

Pit vipers are named for the heat-sensing hollow between each eye and nostril. In experiments, blindfolded rattlesnakes have still struck their prey accurately.

Infrared lasers carry long-distance internet and phone signals through which kind of cable?

Fiber-optic lines use infrared because it travels along the strands with far less loss than electricity in a metal wire, so signals can run long distances between boosts.

Which Apple feature works in the dark by projecting more than 30,000 invisible infrared dots onto its user?

Face ID reads the dot pattern with an infrared camera to build a 3D map of the face. The depth-sensing technology grew out of a body-tracking sensor made for a games console.

Which medical device clips onto a fingertip and shines red and infrared light through it?

A pulse oximeter compares how much of each light gets through, because oxygen-rich blood absorbs more infrared while oxygen-poor blood absorbs more red.

Which burglar-alarm devices, often labelled PIR, are triggered by a person's infrared body heat?

Motion detectors of this kind send out nothing themselves, which is what the P for passive means. They react to the jump from room temperature to body temperature as someone crosses their view.

Every object gives off infrared or other thermal radiation unless cooled to which theoretical temperature?

Absolute zero, about minus 273 degrees Celsius, is the only temperature at which matter would stop radiating, so even an ice cube glows in infrared.

On the electromagnetic spectrum, infrared sits between visible red light and which lower-frequency band?

Microwaves come next as wavelengths lengthen, followed by radio waves. The far edge of infrared blurs into them in the terahertz region, which can be counted as part of either band.

Infrared weather-satellite images let forecasters track the height and type of what throughout the night?

Clouds show up after dark because infrared images map temperature instead of reflected sunlight. High, cold tops such as thunderheads stand out from lower, warmer layers.

NASA's largest infrared space telescope has mirrors coated in which metal for its infrared reflectivity?

Gold coats all 18 hexagonal beryllium segments, which together form a mirror 6.5 metres across, far wider than the one on Hubble.

NASA's SOFIA observatory flew an infrared telescope into the stratosphere aboard which modified airliner?

A Boeing 747 of the shortened SP type, with a large door cut into its fuselage, flew the telescope about 12 kilometres up. The retired jet is now on show at a museum in Arizona.

Infrared telescopes can watch stars being born because infrared passes through which material in space?

Dust soaks up visible starlight but lets longer infrared waves through, opening a view into star-forming regions and the crowded centres of galaxies.

Infrared telescopes are flown on aircraft or built on high peaks to get above which absorbing gas?

Water vapor absorbs much of the infrared arriving from space, so astronomers go to high altitudes, or lift telescopes on balloons, to climb above most of it.

The IRAS infrared space telescope stopped observing after ten months when it ran out of which coolant?

Liquid helium kept the telescope at about minus 271 degrees Celsius so its own warmth would not drown out faint signals. All 73 kilograms had boiled away by November 1983.

Which US heat-seeking missile is named after a desert rattlesnake that itself hunts by sensing infrared?

Sidewinder was picked in 1950 as the name of the AIM-9, an air-to-air missile; the snake it honours finds warm-blooded prey with heat-sensing organs of its own.

Edme Mariotte showed in 1681 that which material, though clear to sunlight, blocks invisible radiant heat?

Glass of the ordinary window kind is opaque to long-wave infrared, which is why a thermal camera cannot see through a window pane.

Thermal camera lenses are often cut from which grey element, opaque to the eye but clear to infrared?

Germanium looks like dull metal yet lets infrared pass, so it can be cut and polished into lenses and windows. Decades earlier, it was the material that launched the transistor age.

Samuel Langley's 1880 bolometer could sense the infrared warmth of which farm animal a quarter mile away?

A cow standing 400 metres off was enough to register on the device, which measured tiny temperature changes in thin metal strips blackened with lampblack.

After the discovery of infrared, Johann Ritter searched the spectrum's other end and found what in 1801?

Ultraviolet turned up when Ritter, hunting for cooling rays to match the heat rays, saw paper soaked in silver chloride darken fastest just outside the visible colours.

In near-infrared landscape photographs, what turns as bright white as snow, giving a dreamlike look?

Tree leaves and grass reflect near-infrared the way snow reflects visible light. Photographers name the look after Robert W. Wood, who published early infrared photographs in 1910.

In 2013 a brain implant gave which laboratory animals a brand-new ability to sense infrared light?

Rats wearing the implant learned to seek out infrared signals, because a sensor on the head fed its output into the touch region of the brain that handles their whiskers.

Infrared ports on laptops and mobiles gave way to which radio standard named after a Danish king?

Bluetooth won out because radio needs no direct line of sight, unlike an infrared beam, so it could link mice and keyboards from any angle.

The IRAS satellite found an infrared-glowing disc of debris around which bright star in Lyra?

Vega gave its name to a whole class: stars that show extra infrared from orbiting debris warmed by the star are still called Vega-like.

Chemists identify molecules by the infrared they absorb, because absorbing it makes their bonds do what?

Vibrate is the word: each kind of bond stretches and bends at its own frequency and absorbs the matching infrared, leaving a pattern chemists read like a fingerprint.

Which US electronics company patented an efficient infrared-emitting diode in 1962, paving the way for LEDs?

Texas Instruments engineers got efficient near-infrared light from a gallium arsenide diode, so the earliest practical LEDs glowed in a colour nobody could see.

Light from the earliest galaxies reaches Earth as infrared after being stretched by what, as space expands?

Redshift moves the visible glow of very distant, very early objects into the infrared, which is why telescopes hunting the first galaxies are built to see those wavelengths.

The astronomer who discovered infrared had earlier found which planet from his garden in Bath, England?

Uranus was first reported as a comet after it was spotted in March 1781. It became the first planet ever identified with the aid of a telescope.

What name did the discoverer of infrared give to the invisible radiation he had found?

Calorific rays was the label chosen in 1800, since the radiation showed itself only as warmth. The word infrared did not appear until late in the 19th century.

Which body-tracking games accessory followed players by projecting a near-infrared pattern across the room?

Kinect for Xbox 360 judged depth from how its projected pattern landed on furniture and people, letting players control games with no controller in hand.

Infrared reflectography lets art conservators study which hidden layer of an old painting without damaging it?

Underdrawing often shows up well because artists tended to sketch it in carbon black. Changes between that outline and the finished paint help tell an original from a copy.